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TECHNICAL BULLETIN 4. 



by which it could make its way into the interior tissues of the plant. A 

 stage of infection has not yet been found so young that the tube has just 

 entered the epidermal cell and has not progressed further. 



Passage through the Epidermal Cells. 

 In the youngest infections observed, the mycelium had already grown 

 through the epidermal cells, and its tips could be found in the intercellular 

 spaces at a depth of two or more layers below. In some cases a piece of 

 the infecting hypha still remained on the exterior of the cuticle, but was 

 always devoid of contents and consisted only of somewhat crumpled walls 



Fig. 4. — Infection through the epidermal cells; A, B, C from outside the cotyledon, D from 

 the cotyledonary cavity. 



(Fig. 4), A broad clear canal passes inward from the outer wall usually 

 directed toward the cell nucleus. The wall of the canal appears to be 

 continuous with the cell wall as if merely an inward extension of the same. 

 Commonly it is much thicker at the point of entrance, and resembles a 

 slender funnel or trumpet in shape. It was not found possible to deter- 

 mine whether part of the wall of the canal is an inward growing sheath of 

 the same substance as the cell wall, or whether it is merely a thickened 

 wall of the hypha. In all the cases observed, the canal was empty at the 

 point of entrance. The host nucleus appears to exert an attractive influ- 

 ence. When the tube has reached the depth of the nucleus, it branches 

 to form a tangle of stout, swollen, gnarled, hyphse which maj^ be confined 

 to the region immediately about the nucleus, or may reach to all parts of 

 the lumen of the host cell (Fig. 4). They may be entirely devoid of con- 



